Hi Guennadi,
On Thursday 17 February 2011 17:46:15 Guennadi Liakhovetski wrote:
> Hi all
>
> Let me try to further elaborate on this topic. So far, I think, the
> following provides the cleanest solution to our quick format-switching /
> multiple video-queue problem:
>
> On Wed, 16 Feb 2011, Guennadi Liakhovetski wrote:
> > (2) cleanly separate setting video data format (S_FMT) from specifying
> > the allocated buffer size.
>
> The control flow then would look like:
>
> struct v4l2_requestbuffers req;
>
> fd = open();
>
> /* initialise and configure the first "still-shot" buffer-queue */
> bufq.id = -EINVAL;
> ret = ioctl(fd, VIDIOC_BUFQ_SELECT, &bufq);
If we're going to introduce new ioctls, I think we should do it right from the
start. Your proposal looks like an interim solution that would be deprecated
when buffer pools will be implemented. I think we should work directly on
buffer pools instead.
> /*
> * bufq.id now contains a handle to a newly allocated videobuf
> * queue, it also becomes the current queue.
> */
>
> still_qid = buf.id;
>
> /*
> * specify explicitly required buffer size - use one of reserved
> * fields
> */
> req.size = still_x * still_y * bpp;
> ret = ioctl(fd, VIDIOC_REQBUFS, &req);
>
> for (i = 0; i < req.count; i++) {
> buf.index = i;
> ret = ioctl(fd, VIDIOC_QUERYBUF, &buf);
> start = mmap();
> ret = ioctl(fd, VIDIOC_QBUF, &buf);
> }
>
> /* Allocate a second "preview" queue */
>
> bufq.id = -EINVAL;
> ret = ioctl(fd, VIDIOC_BUFQ_SELECT, &bufq);
>
> preview_qid = bufq.id;
>
> req.size = preview_x * preview_y * bpp;
> ret = ioctl(fd, VIDIOC_REQBUFS, &req);
>
> for (i = 0; i < req.count; i++) {
> buf.index = i;
> ret = ioctl(fd, VIDIOC_QUERYBUF, &buf);
> start = mmap();
> ret = ioctl(fd, VIDIOC_QBUF, &buf);
> }
>
> /* Stay on the preview queue */
> ret = ioctl(fd, VIDIOC_STREAMON, &type);
>
> for (i = 0; i < n; i++) {
> ret = ioctl(fd, VIDIOC_DQBUF, &buf);
> ret = ioctl(fd, VIDIOC_QBUF, &buf);
> }
>
> ret = ioctl(fd, VIDIOC_STREAMOFF, &type);
>
> /* Switch to the still-shot queue */
> bufq.id = still_qid;
> ret = ioctl(fd, VIDIOC_BUFQ_SELECT, &bufq);
>
> ret = ioctl(fd, VIDIOC_STREAMON, &type);
>
> for (i = 0; i < n; i++) {
> ret = ioctl(fd, VIDIOC_DQBUF, &buf);
> ret = ioctl(fd, VIDIOC_QBUF, &buf);
> }
>
> ret = ioctl(fd, VIDIOC_STREAMOFF, &type);
>
> And so on. If the above is _conceptually_ acceptable, we need 1 to 2 new
> ioctl()s and an extension to the VIDIOC_REQBUFS ioctl() to specify the
> buffer size. I wrote "1 or 2 new ioctl()s," because above the new
> VIDIOC_BUFQ_SELECT ioctl() performs two functions: if the handle is
> negative, it allocates a new queue, if it containes a valid (per-device or
> per file-handle?) queue ID, it switches to it. We might also decide to use
> two ioctl()s for these two functions.
--
Regards,
Laurent Pinchart
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